1. Field of the Invention
The present invention generally relates to ignition circuits and, more particularly, to ignition circuits and systems for portable power tools.
2. Description of Related Art
Portable power tools such as chain saws, string trimmers, hedge trimmers, edgers, and blowers typically have two-stroke gasoline engines which require manual choking to provide a fuel rich mixture to the engine during manual cold starting thereof. Such power tools conventionally include a manually-operated choke assembly and a separate ignition or "kill" switch. The ignition switch is manually movable between an ignition or run position wherein ignition of fuel within the engine is permitted and a stop position wherein ignition is prevented. The ignition switch is primarily provided to allow the operator to turn the power tool off when desired.
Traditionally, manual operation of the choke assembly to supply a fuel-rich mixture to the engine, which facilitates cold starting of the power tool, is completely separate from the necessary re-setting of the ignition switch to the run position. It has been found that, while the operator normally remembers to operate the choke assembly, he or she quite often forgets to manually move the ignition switch to the run position before attempting to start the engine.
Failure to place the ignition switch in the run position prevents starting of the power tool and, due to the oversupply of fuel to the engine, the engine is eventually flooded. Flooding of the engine makes starting of the engine difficult or impossible should the operator subsequently place the ignition switch in the run position, and typically forces the operator to wait a period of time until the "flooded" condition of the engine has been resolved.
In response to this problem, several solutions have been proposed. One solution, set forth in U.S. Pat. No. 2,791,207, utilizes a combined choke and ignition or kill switch actuator. The actuator is moved in or out to adjust the choking of the engine, and is rotated to move the ignition switch between the run and off positions. When the actuator is in the run position and is pulled out to choke the engine, it cannot be rotated to the "off" position. Similarly, when the actuator is in the "off" position, it cannot be pulled out to choke the engine.
Another solution is presented in U.S. Pat. No. 5,209,196. The '196 patent discloses an operating mode selector which includes an ignition switch. The mode selector is movable between various positions, such as off, idle, cold start, and warm start. The ignition switch is connected to the throttle and choke flaps via linkages. U.S. Pat. Nos. 4,079,708 and 5,215,049 show other selector switches which control positioning of the throttle and choke flaps.
Another approach to solving the problem presented by operators trying to start the engine without placing the ignition switch in the run position is set forth in U.S. Pat. No. 4,919,091. The '091 patent discloses a device for automatically resetting an ignition switch unit to the run or start position. The ignition switch unit includes a latching member which is biased to the start position. A positioning member, which includes the user-engagable ignition switch, engages the latching member and holds the latching member in the "off" position. When the engine coasts to a standstill, the positioning member disengages the latching member and allows the latching member to move to its at-rest or start position. A second embodiment of the '091 includes a push actuator which can be latched in a position to disable ignition.
The aforementioned patents disclose various devices and methods for preventing the operator from neglecting to reset the ignition switch from the stop to the run position. However, the solutions posed by these patents are typically expensive to implement, and result in more costly portable power tool. Moreover, the integration of the operation of the ignition switch and choke into a single selector switch, as taught by some of these patents, is undesirable for operators who have grown accustomed to choke assemblies and ignition switches which are separate and independently operable. Finally, the selector switches or mechanisms taught by some of these patents may be difficult for the operator to quickly locate and operate should operation of the power tool need to be quickly terminated.
Therefore, there exists a need in the art for a simple and inexpensive device which operably links the choke assembly and the kill switch whereby operation of the choke assembly to supply a fuel-rich mixture to the engine necessarily moves the ignition switch into the run position and allows starting of the power tool. There also exists a need in the art for device which allows independent operation of the ignition switch when the choke assembly is in its normal or non-choking position. Finally, there exists a need in the art for a device which appears to be a conventional power tool having an ignition switch which is operable independently of a choke assembly, but in which the choke assembly is operably linked to the ignition switch so that the ignition switch is automatically moved to the run position when the choke assembly is moved from a non-choking to a choking position.